Four protesters have been killed in clashes that erupted today during marches in Cairo and across Egypt on the anniversary of the uprising that toppled former president Hosni Mubarak.

Witnesses said Egyptian police fired live rounds in the air earlier, along with tear gas to disperse about 1,000 anti-government protesters in Cairo's Mohandiseen district and at two other marches in downtown.

Supporters of the military-backed government, led by General Abdel Fatah al-Sisi, gathered in Tahrir Square today to celebrate the anniversary, one day after four explosions rocked Cairo, targeting police buildings and vehicles in a series of attacks that killed at least six people and injured over fifty.

An al-Qa'ida-inspired group, based in the lawless Sinai Peninsula, claimed responsibility, according to the SITE monitoring organization.

Egypt actor turned activist talks about revolution and patience in this video

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Some of the demonstrators were supporters of the Brotherhood, while others were liberal activists. Witnesses said police also fired tear gas and birdshot at a crowds of activists moving toward Tahrir for an anti-government rally. Dozens of anti-government protesters were also arrested in Egypt's second city Alexandria, security sources said.

Security has been tight in the capital following clashes across Egypt on Friday that left 18 people dead.

A bomb was thrown at the wall of police training academy in Cairo shortly before 6am GMT this morning, injuring one person, according to reports. No one has claimed responsibility for the attack.

Sisi toppled Islamist President Mohamed Morsi on 3 July following mass protests against his rule. The Brotherhood has been declared a terrorist organisation by Egypt's military-backed interim government, criminalising all its activities, its financing and even membership to the group.

The general, who served as head of military intelligence under Mubarak, is expected to announce his candidacy for the presidency soon and likely to win by a landslide in elections, expected within six months.

Several leading politicians have indicated they would not run for president if Sisi does, highlighting his dominance and the barren political landscape that has emerged since Mubarak's fall. The most vocal critics of the new order - the Brotherhood - have been driven underground.